Sensitometry Theory - Links to useful materials

Stephen Benskin · Apr 6, 2015

Bill Burke has kindly posted a number of the papers all in one place http://beefalobill.com/benskin/. These include:

Allen Stimson, An interpretation of Current Exposure Meter Technology
D. Connelly, Calibration Levels of Film and Exposure Devices
C.J. Niederpruem, C.N. Nelson, and J.A.C Yule, Contrast Index
Defining K, compiled by Stephen Benskin
B.E. Bayer, J.L. Simonds, and F.C. Williams, Description of D-log E Curves by Specifically Chosen Parameters
G.S. Allbright, Emulsion Speed Rating Systems
J. F. Scudder, C.N Nelson, Allen Stimson, Re-evaluation of Factors Affecting Manual or Automatic Control of Camera Exposure
C.N. Nelson and J.L. Simonds, Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials
H.N. Todd and R.D. Zakia, Tutorial: A Review of Speed Methods
C.N. Nelson, Safety Factors in Camera Exposures

chriscrawfordphoto · Apr 6, 2015

Cool! Thanks for this

superpos · Apr 7, 2015

interesting papers, many thanks for the link!

Stephen Benskin · Apr 7, 2015

superpos said:
interesting papers, many thanks for the link!

A couple of the papers are seminal. Safety Factors and Simple Methods for Approx. Fractional Gradient lead to the 1960s black and white film speed standard. Contrast Index introduced contrast index. Interpretation of Current Exposure Meter Technology and Re-evaluation of Factors Affecting Manual or Automatic Control of Camera Exposure preceded the 1971 exposure meter standard. Calibration Levels of Film and Exposure Devices explains the relationship between metered exposure and film speed.

ic-racer · Apr 7, 2015

A good project for someone would be to paraphrase the seminal papers to make the info more accessible to the average APUG user. I know there are book chapters that pull the info together, but posting book chapters could violate copyright laws.

Photography is a unique expression that straddles art and science. A painter does not need to know the chemical composition of the paint, but a photographer needs to know the physics behind exposure and development. Understanding exposure and development is the difference between a snapshooter and someone in control of their work.

K-G · Apr 7, 2015

superpos said:
interesting papers, many thanks for the link!

+1

Karl-Gustaf

fotch · Apr 7, 2015

Stephen Benskin · Apr 7, 2015

ic-racer said:
A good project for someone would be to paraphrase the seminal papers to make the info more accessible to the average APUG user. I know there are book chapters that pull the info together.

Wouldn't diluting the information eliminate the whole purpose of having source material?

MattKing · Apr 7, 2015

Thanks for the better thread title

Bill Burk · Apr 8, 2015

Happy to provide a home for these important papers. They're all Stephen's collection, so he deserves the thanks.

Neer Taliyan · Apr 8, 2015

Thanks for this

Stephen Benskin · Apr 8, 2015

Four more have been uploaded

Contrast Measurement of Black and White Negative Materials
J.F. Dunn, Expose for the Middle Tones
J.L. Simonds, Factors Affecting the Quality of Black and White Reflexion Prints
Holm, Jack, Exposure Speed Relations and Tone Reproduction

Factors Affecting the Quality of B&W Reflexion Prints has a section on flare and long and short toed films that is interesting. Holm's paper has a great section on the mathematical framework of exposure. Be careful though with his Zones of the Zone System table. He uses a range that is based off of 128% for highlight reflectance and not 100%. Holm's has crammed a lot into eight pages.

Stephen Benskin · Apr 10, 2015

ic-racer said:
A good project for someone would be to paraphrase the seminal papers to make the info more accessible to the average APUG user. I know there are book chapters that pull the info together, but posting book chapters could violate copyright laws.

Photography is a unique expression that straddles art and science. A painter does not need to know the chemical composition of the paint, but a photographer needs to know the physics behind exposure and development. Understanding exposure and development is the difference between a snapshooter and someone in control of their work.

I think I have an example of the potential insight that comes from reading the source material. Equation 3 in Safety Factors in Camera Exposure (found in the link on post #1) describes the American Standard formula for the film exposure index from the pre 1960 ASA standard.

Z = k / Es

where:
Z = American Standard exposure index
k = 1/4
Es = the exposure in meter-candle-seconds required to obtain a specific minimum response on the film as determined by the fractional gradient speed criteron (American Standard Speed = 1/Es)

The fractional gradient speed point (Es) falls almost 1 stop to the left of the fixed density point of 0.10 over Fb+f. A modern rated 125 speed film has an exposure of 0.0064 mcs at 0.10 density. That would make the exposure for the film 0.0032 at the fractional gradient speed point. Plugging 0.0032 into the above equation produces an exposure index of:

0.25 / 0.0032 = 78

The film's speed using American Standard Speed criterion would be:

1 / 0.0032 = 312.5

So even though the fractional gradient's speed point is one stop to the left of the 0.10 fixed density speed point, using an exposure constant of 0.25 creates a film speed 2/3 stop slower than what the post 1960 ASA standard and current ISO film speed criterion would produce.

What this implies is that where the speed point is measured isn't necessarily where the shadow is supposed to fall. That the placement has other significance. This concept is reinforced later under the Proposed Change in Speed Criterion section. "The reduction in the safety factor could be accomplished simply by changing the constant in the ASA formula for deriving the ASA exposure index from the ASA fractional gradient speed of the film...If the constant of 1/4 were replaced by a constant of 1/2, a new type of 'exposure index' would be obtained which would provide the proposed lower safety factor of about 1.2."

The current ISO standard's speed equation is 0.8 / Hm. What are the implications of using 0.8 for the exposure constant and not 1.

The fractional gradient point represents the limiting gradient that will produce a high quality print. Anything below, the quality will be diminished, but there's a range above the point where quality remains excellent.

Another section, starting with equation 4 and ending with equation 9, is the rational for the metered exposure constant P = 8 (also known as K1 in the exposure meter standard).

Bill Burk · Apr 10, 2015

Sorry to bear bad news but I hit bandwidth quota on my little vanity site...

For lack of a better idea, I just hid the documents for now.

Soon as I figure out a way, I'll try to bring these back online.

Bill Burk · Apr 12, 2015

At least until I figure out a permanent solution...

The files are hosted somewhere else...

Please try the original link again it will take you to the files after a couple hoops.

Bill Burk · Apr 12, 2015

The new location has limited connections, so if you see "try again later" message, it is to be expected and means what it says...

Stephen Benskin · Apr 13, 2015

Bill Burk said:
The new location has limited connections, so if you see "try again later" message, it is to be expected and means what it says...

Thank again Bill for all the effort you've put into making these papers available.

Auroraua · Apr 21, 2015

What is the link to these papers?
Thanks for this.

Bill Burk · Apr 21, 2015

Auroraua said:
What is the link to these papers?
Thanks for this.

The first post of this thread gives the URL. Then follow link instructions (intended to block robots).

JPJackson · Apr 23, 2015

Thank you Stephen and Bill for putting this together.

swmcl · Apr 27, 2015

Bill,

You are a sneaky chap with the word content eh !

Well done.

I now have a copy and I would also like to express gratitude for the collation. If I could assist a little, you may get a fair saving in bandwidth if you made available just the one zip file.

It highlights the fact that there has been a lot of serious academic work in analogue photography that is very much in danger of being lost if people don't digitize what they find and get it into the www. I can't imagine more than 10 readers worldwide but still ... !!

Thanks again,

Steve

ps. if you want another site perhaps I could help - just message me.

RalphLambrecht · Apr 27, 2015

ic-racer said:
A good project for someone would be to paraphrase the seminal papers to make the info more accessible to the average APUG user. I know there are book chapters that pull the info together, but posting book chapters could violate copyright laws.

Photography is a unique expression that straddles art and science. A painter does not need to know the chemical composition of the paint, but a photographer needs to know the physics behind exposure and development. Understanding exposure and development is the difference between a snapshooter and someone in control of their work.

I should frame this and put it up on the wall!

Raghu Kuvempunagar · Jul 29, 2021

Stephen Benskin said:
Bill Burke has kindly posted a number of the papers all in one place http://beefalobill.com/benskin/. These include:

Allen Stimson, An interpretation of Current Exposure Meter Technology
D. Connelly, Calibration Levels of Film and Exposure Devices
C.J. Niederpruem, C.N. Nelson, and J.A.C Yule, Contrast Index
Defining K, compiled by Stephen Benskin
B.E. Bayer, J.L. Simonds, and F.C. Williams, Description of D-log E Curves by Specifically Chosen Parameters
G.S. Allbright, Emulsion Speed Rating Systems
J. F. Scudder, C.N Nelson, Allen Stimson, Re-evaluation of Factors Affecting Manual or Automatic Control of Camera Exposure
C.N. Nelson and J.L. Simonds, Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials
H.N. Todd and R.D. Zakia, Tutorial: A Review of Speed Methods
C.N. Nelson, Safety Factors in Camera Exposures

@Bill Burk: your site seems to be not working. Are these papers available together anywhere else?

Adrian Bacon · Jul 29, 2021

Raghu Kuvempunagar said:
@Bill Burk: your site seems to be not working. Are these papers available together anywhere else?

@Bill Burk @Stephen Benskin I have a pretty hefty hosting solution for hosting client film scans, it’d be pretty trivial to make a dedicated directory and park the documents there for everybody to download as they wish if that’s something you’d be interested in doing. It’s backed by Amazon S3 and Cloudfront so it’s super high bandwidth and super redundant, and I doubt it’d be so much monthly traffic that I cared about it as I move data by the terabyte at the per month level. Shoot me a PM if you want to discuss.

Sensitometry Theory - Links to useful materials

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